1. Field of the Invention
The present invention relates to the shaping of glass sheets, and particularly to hydraulic fluid actuated pistons which are used to actuate movement of glass sheet shaping molds having a shaping surface of predetermined configuration for movement between a glass-engaging position to change the shape of a heat-softened glass sheet, and a retracted position to permit the mold to await the arrival of a glass sheet into a position where it can be engaged by the moving shaping mold. In mass production operation, it is necessary that the mold movement is smooth and of controlled speed from cycle to cycle so as to insure uniform application of pressure against the heat-softened glass sheet so as to insure that each glass sheet which is shaped in turn is shaped to a curvature that conforms as uniformly as possible to the shape imparted to every other glass sheet in a series of glass sheets shaped in a mass production operation.
Typically, a hydraulically operated piston divides a piston cylinder into two chambers and hydraulic fluid is applied under pressure alternately to each of the opposite chambers and simultaneously removed from the other chamber. Prior to the present invention, the hydraulic fluid removed from one of the chambers was fed directly into the other chamber and as a result, the hydraulic fluid tended to become hot. The hot hydraulic fluid tended to carbonize and also to foam or bubble. Such factors cause the hydraulic fluid to operate haphazardly instead of uniformly and steadily, thereby resulting in non-uniform operation of the piston. It was difficult, if not impossible, to coordinate the movement of the shaping mold with the introduction of a heat-softened glass sheet into a glass sheet shaping station where the shaping mold moved in response to actuation by the piston operating with hot hydraulic fluid from a retracted position into a glass-engaging position to impart a desired shape to the glass sheet. It was therefore desirable to develop a technique that would insure better uniformity of operation of glass sheet shaping molds than the haphazard and unpredictable operation of mold movement actuated by pistons whose cylinders contain hot hydraulic fluid that incorporated foam and/or carbon particles resulting from its heating during mass production bending operations.
2. Description of Patents of Interest
U.S. Pat. No. 840,876 to Steedman discloses a hydraulic system for double acting piston actuators which have regulated lines for one-way flow of branch lines into and out of chambers on both sides of the piston within the piston cylinder. However, the double flow lines are used for pressure regulation and not for cooling purposes.
U.S. Pat. No. 3,000,357 to Geyer discloses a high temperature hydraulic actuator assembly which is proposed to avoid the necessity of continuously circulating hydraulic fluid through parts exposed to ambient temperatures in the range of 1000.degree. F. to cool hydraulically operated actuators at such elevated temperatures. Differential pressure is applied through both the extend valves and the retract valves to permit oil to be continuously circulated whenever the hydraulic actuator is operated in a high temperature environment, thus providing a cooling effect.
U.S. Pat. No. 3,294,516 to Carson et al discloses a hydraulic system for actuating movement of a glass sheet bending mold. Reservoirs are provided with the hydraulic supply system. However, no mention is made of any technique for cooling the hydraulic fluid in this patent.
U.S. Pat. No. 4,073,311 to McGeachy discloses a bi-directional valve for unrestricted flow in one direction and a regulatable restriction for flow control in the other direction which includes control valves permitting hydraulic fluid movement in one or the other direction. The control lines are used for pressure regulation annd not cooling purposes in this patent.
U.S. Pat. No. 4,119,427 to Revells discloses a hydraulic system for controlling the operation of a piston which controls the vertical movement of a glass sheet shaping mold. Means is provided to store hydraulic fluid. However, no mention is made of cooling the hydraulic fluid in this patent.